This invention relates to a print cartridge and an image forming apparatus, such as an electrophotographic copying machine and a printer, provided with such a print cartridge.
In a known image forming apparatus, image forming devices, such as a primary static charger, an image exposing portion, a developing device, a transfer static charger and a cleaner, are arranged around the periphery of an image bearing member. After the surface of the image bearing member is electrostatically charged uniformly by the primary static charger, the image is exposed to form an electrostatic latent image, and this electrostatic latent image is developed by the developing device into a visible image. This visible image is transferred to paper by the transfer static charger. The paper is fed to a fixing device for fixing purposes, and the residual toner on the image bearing member is cleaned off by the cleaner.
In such an image forming apparatus, the lifetime of the image bearing member as well as the lifetime of the image forming devices is short, and they need to be periodically inspected, repaired and exchanged. For example, as disclosed in Japanese Laid-Open (Kokai) Patent Application No. 65049/87, an image bearing member and some of image forming devices are integrally formed into a print cartridge, and the print cartridge is removably attached to the body of the apparatus, thereby facilitating inspection, repair and exchange operations.
It is important that the image bearing member of such a print cartridge should be driven at a constant speed during the image forming operation in order to achieve an image formation free from a cyclic deviation. Therefore, it is necessary that a drive shaft supported on the body of the apparatus should be connected to the image bearing member without any misalignment and play.
For example, as shown in the above-mentioned Japanese Laid-Open Patent Application No. 65049/87, a shaft support hole is formed in a flange of the image bearing member at the axis of rotation of the flange, and an engaging hole is formed around the periphery of the shaft support hole, and a power transmit member is mounted on the drive shaft supported on the apparatus body. When the print cartridge is inserted into the apparatus body, the shaft support hole fits on the distal end of the drive shaft, and at the same time a projection of the power transmit member fits in the engaging hole, thereby connecting the image bearing member and the drive shaft together coaxially with each other so that the drive shaft can rotate the image bearing member.
In the above prior art, however, since the flange is integrally formed by a resin, the flange must be increased in diameter because of its insufficient rigidity, and as a result the diameter of the image bearing member can not be made small. Further, the drive shaft is made of iron-type metal whereas the flange is made of a resin, and therefore the difference in thermal expansion coefficient between the two is large. In view of this, if a gap between the drive shaft and the shaft support hole is increased, the play of the image bearing member is increased, so that the print quality is degraded. In contrast, if the gap between the drive shaft and the shaft support hole is decreased, this makes it difficult to remove the print cartridge in a low-temperature environment. Further, in the prior art, since the flange is made entirely of a resin, an earth connection must be taken via the drive shaft. Therefore, an earth slide portion connecting the drive shaft to the apparatus body must be provided, and this earth slide portion need to be periodically exchanged because of its short lifetime.
In order to overcome these problems, it is considered that the flange is made entirely of metal; however, in such a case, the weight of the print cartridge is increased, and a large force is required when exchanging the print cartridge, and also the cost is increased.